A semiconductor device manufacturing method includes: removing an insulating film on a semiconductor substrate by using wet etching and subsequently oxidizing a surface of the substrate by using a liquid oxidation agent without exposing this surface to an atmosphere, thereby forming a first insulating film containing an oxide of a constituent element of the substrate on the surface of the substrate; forming a second insulating film containing aluminum and another metal element on the first insulating film; forming a high-k insulating film containing at least one of hafnium and zirconium on the second insulating film; forming a metal film on the high-k insulating film; and conducting heat treatment to react the first insulating film and the second insulating film, thereby forming a third insulating film made of a mixture containing aluminum, the another metal element, the constituent element of the substrate, and oxygen.